Key numbers
238 deaths
Deaths over 13 years in the Canadian cohort of 8116 adults
72.9 years
Mean age of the Taiwanese cohort
What the studies counted as flexibility
Katzmarzyk and colleagues (2002) measured sit-ups, push-ups, grip strength and sit-and-reach trunk flexibility. Wu and colleagues (2026) used seven tests across four areas (cardiorespiratory fitness, muscular strength, flexibility, and balance and agility), measuring flexibility with the back scratch and chair sit-and-reach tests.
Did flexibility track mortality?
The Canadian cohort followed 8116 people from the 1981 Canada Fitness Survey, aged 20 to 69 at the start, for 13 years: 101,685 person-years and 238 deaths. People were grouped into quartiles for their age and sex. For trunk flexibility there was no pattern of higher death rates across the quartiles.
The Taiwanese cohort was community-dwelling adults aged 65 or older, mean age 72.9, followed for a median of 7.0 years, during which 12.2 percent died. Physical fitness, particularly balance and agility, lower-body strength and cardiorespiratory fitness, was associated with lower death rates in a graded way. Flexibility was not among the four tests with clear links.
What did show a link in those studies
In the Taiwanese cohort, people in the best fifth of results had lower death rates than those in the worst fifth on four tests: the 8-foot up-and-go (adjusted hazard ratio 0.41, 95 percent CI 0.33 to 0.51), the 1-leg stance (0.50, 0.42 to 0.59), the 30-second chair stand (0.55, 0.46 to 0.65) and the 2-minute step test (0.58, 0.49 to 0.68).
These are associations in groups of people. They do not show that any of these capacities causes a longer life, and they do not mean flexibility is unimportant. None of these tests is the Systematic assessment.
The evidence
Each cited source is labeled according to how it supports the particular claim on this page. Direct test evidence, underlying-capacity findings and population reference values are distinguished from Systematic-defined protocols and standards. Historical development notes are retained internally rather than presented as public evidence. A study of an underlying capacity is never presented as validation of the Systematic test itself.
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Underlying-capacity evidence New source
Katzmarzyk et al. (2002). Musculoskeletal fitness and risk of mortality. Medicine and science in sports and exercise.
What it found. Among 8116 Canadians aged 20 to 69 (238 deaths over 13 years), sit-and-reach flexibility showed no pattern of higher mortality across quartiles.
What it does not show. A null result in one cohort does not prove flexibility has no benefit, and it does not show cause.
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Underlying-capacity evidence New source
Wu et al. (2026). Physical Fitness and All-Cause Mortality in Older Adults. JAMA network open.
What it found. In Taiwanese adults aged 65 or older, four tests (up-and-go, 1-leg stance, chair stand, 2-minute step) showed clear highest-versus-lowest links with lower mortality; flexibility was not among them.
What it does not show. It does not show that all seven tests tracked mortality, and the battery does not validate Systematic's different tests.
The Systematic Healthspan Assessment is a physical baseline. It is not a diagnosis, and it does not estimate a biological age, a disease risk or a lifespan.